The present invention relates to an outboard motor and, more particularly, a device for lubricating an inside portion of an engine unit of an outboard motor with oil.
An outboard motor has an engine unit mounted vertically in such a way that the crank shaft of the engine is vertically disposed. The engine is formed by assembling a crank case, a cylinder block, a cylinder head and the like. If the engine is a four-stroke-cycle engine, an oil pan is disposed below the engine. A lubricating device having an oil pump for pumping up oil accumulated in the oil pan is provided to lubricate the inside portion of the engine.
As a conventional lubricating device for an outboard motor, the following lubricating devices have been provided as disclosed in, for example, Japanese Patent Laid-Open Publication No. HEI 8-100614 (hereinafter called a "first conventional example"), Japanese Patent Publication No. 2516024 (hereinafter called a "second conventional example"), Japanese Patent Laid-Open Publication No. HEI 7-94803 (hereinafter called a "third conventional example") and Japanese Patent Laid-Open Publication No. HEI 3-38156 (hereinafter called a "fourth conventional example").
The lubricating device according to the first conventional example has a structure in which an oil pan is attached below a cylinder block and a cylinder head. An oil pump is disposed below the cylinder head in the oil pan 88, and the oil pump is operated by a cam shaft rotatably supported in the cylinder head.
The lubricating device according to the second conventional example has a structure in which an oil pan is attached below a cylinder block. An oil pump is disposed below a cylinder head which serves as the outer surface of the oil pan so that the oil pump is operated by a cam shaft. An oil discharge passage extending from the oil pump is formed in the core portion of the cam shaft and the inside portions of the cylinder block and the cylinder block. An oil-pressure control valve is disposed in a portion in which the oil discharge passage passes through the inside portion of the cylinder block. An oil strainer connected to the suction portion of the oil pump is attached to the lower surface of the cylinder block.
The lubricating device according to the third conventional example has a similar structure in which an oil pump is disposed below a cylinder head at a position on the outside of the oil pan. Thus, the oil pump is operated by a cam shaft. In this example, oil suction passages extending from the oil pump and oil returning passages for returning, to the oil pan, oil supplied to the inside portion of the cylinder head are formed from the cylinder head to a cylinder block. A hose for returning oil extends from the head cover, the hose being joined to the oil returning passage. Moreover, an oil strainer is attached to the lower surface of the cylinder block.
The lubricating device according to the fourth conventional example has a structure in which an oil pump disposed on the lower surface of a cylinder head is operated by a cam shaft. An oil discharge passage extending from the oil pump is formed from the cylinder head to a cylinder block. An oil-pressure control valve connected to an intermediate position of the oil discharge passage is disposed on the lower surface of a plate secured to the lower surface of the engine.
However, the conventional lubricating devices for the outboard motors according to the above-mentioned four conventional examples suffer from the following problems.
Since each of the lubricating devices for an outboard motor has the structure in which the oil pump is disposed on the lower surface of the engine, when the engine is solely removed from the outboard motor for maintenance thereof or the like, it is removed with the oil pump projecting over the lower portion of the engine. Thus, there is a possibility that the oil pump is broken attributable to an external factor. Moreover, the engine cannot be placed on a flat workbench to perform the maintenance. Thus, the maintenance cannot easily be performed.
The lubricating devices according to the second and third conventional examples are structured such that the oil suction passage and the oil discharge passage extending from the oil pump are formed in the cylinder head and the cylinder block of the engine. Therefore, the structure of a mold for casting each of the cylinder head and the cylinder block becomes too complicated to easily manufacture the engine. In particular, the lubricating device according to the third conventional example has the oil returning passages formed in the cylinder head and the cylinder block in addition to the oil suction passages. Moreover, the hose extending from the head cover is joined to the oil returning passage. Therefore, it is more difficult to manufacture the engine of this type, and the size of the engine cannot easily be reduced.
The lubricating device according to the second conventional example has the structure in which the oil-pressure control valve is disposed, together with the oil pump, on the lower surface of the engine. Therefore, when the engine is solely removed from the outboard motor, the oil-pressure control valve may be broken as well as the oil pump. Since the lubricating device according to the fourth conventional example has the structure in which the oil-pressure control valve is disposed on the lower surface of a plate secured to the lower surface of the engine, the oil-pressure control valve cannot be broken when the engine is solely removed in such a manner that the plate is left. However, the oil-pressure control valve may be broken when the engine is removed together with the plate.
The lubricating devices according to the second and third conventional examples have the structure in which the corresponding oil strainers are attached to the lower surfaces of the cylinder blocks. Therefore, the oil strainers must be removed for the purpose of preventing breakage when the engine is removed solely. Therefore, the maintenance easiness further deteriorates.
The lubricating devices according to the second and fourth conventional examples have the structure in which each of the oil discharge passages extending from the oil pumps penetrates a junction between the cylinder head and the cylinder block. Moreover, each of the oil-pressure control valves is disposed in the downstream portion of each of the oil discharge passages. Therefore, there is a possibility that oil leakage takes place from the oil discharge passages in the junction between the cylinder head and the cylinder block.